1. Field of the Invention
This invention relates to a fuel supply control system for internal combustion engines, which operates to increase the amount of fuel to be supplied to the engine when a high load condition of the engine is detected.
2. Prior Art
In a conventional fuel supply control system for internal combustion engines, when the engine enters a predetermined high load condition, a fuel amount supplied to the engine is increased by multiplying a basic fuel amount by a predetermined coefficient, to thereby enrich the air-fuel ratio of a mixture supplied to the engine, immediately after the opening of a throttle valve of the engine exceeds a predetermined value corresponding to the predetermined high load condition, or upon the lapse of a predetermined time period (e.g. approximately 1 second) after the absolute value of pressure within the intake pipe of the engine exceeds a predetermined value corresponding to the predetermined high load condition. By virtue of this increase of the fuel supply amount, not only the engine output can be increased in the high load condition, but also the combustion temperature of the engine can be lowered to prevent a rise in the temperature of a catalyst arranged in the exhaust system of the engine, to thereby prevent the catalyst from being deteriorated or damaged by heat.
Further, an air-fuel ratio feedback control system is known, e.g. from Japanese Laid-Open Patent Publication (Kokai) No. 53-8427, which increases the fuel supply amount by terminating air-fuel ratio feedback control when the pressure of intake air into the engine continuously exceeds a predetermined value over a predetermined time period. As a result, even when the engine is in a high rotational speed and high load condition in which an increased intake air amount is supplied to the engine, a high engine output can be obtained and good performance of the catalyst can be maintained.
According to the conventional fuel supply control systems, however, when it is determined that the engine is in the high load condition, the increase of the fuel supply amount is carried out even if the catalyst temperature is low and does not reach a value at or above which the catalyst can be deteriorated or damaged by heat. This is disadvantageous in respect of exhaust emission characteristics and fuel economy.